Conventionally, there is known a bearing device for wheels that rotatably supports a wheel in a suspension device for an automobile or the like. In the bearing device for wheels, a hub ring connected to the wheel is rotatably supported by an outer member via rolling elements. The bearing device for wheels is secured to a knuckle of a vehicle via a mounting flange of the outer member. In other words, the bearing device for wheels rotatably supports the hub ring connected to the wheel in a state in which the outer member is secured to the knuckle of the vehicle. For the bearing device for wheels, a multi-row angular contact ball bearing with desired bearing stiffness and low rotary torque in view of improvement of fuel consumption is most commonly used. The bearing device for wheels configures the angular contact ball bearing by giving a predetermined contact angle to the rolling elements to thus cause the rolling elements to be brought into contact with the outer member and the hub ring. The outer member of the bearing device for wheels is provided with rolling surfaces for rows of the rolling elements, near an opening on a side of a wheel mounting flange of the hub ring (outer side) and near an opening on a side of a mounting flange of the outer member (inner side). The outer member supports a load from the wheel with the rolling surfaces via the rolling elements that support the hub ring.
In such a bearing device for wheels, when the vehicle stops or moves forward or backward, a load from the vehicle works on the substantially center of the multi-row angular contact ball bearing. On the other hand, when the vehicle turns, a radial load and an axial load exerted on the wheel on a side opposite to a turning direction (a left side of the vehicle when the vehicle turns right) increase. Thus, some bearing devices for wheels increase bearing stiffness by improving stiffness of the row of rolling elements on the outer side to thus prevent deterioration in rolling fatigue life. One example is described in Patent Document 1.
In the bearing device for wheels described in Patent Document 1, the number of rolling elements in a row of rolling elements on an outer side is increased by setting a pitch diameter of the row of rolling elements on the outer side to be larger than a pitch diameter of a row of rolling elements on an inner side, out of multiple rows of rolling elements, and thus stiffness of the row of rolling elements is improved. However, according to this bearing device for wheels, as the pitch diameter of the row of rolling elements on the outer side is increased, a diameter of an opening of the outer member on the outer side is also increased. Further, each opening of the outer member includes a fitting portion for providing a sealing member that prevents rain water or the like from entering into the outer member, a reference surface for processing, and the like. Therefore, the bearing device for wheels has possibilities that, when the radial load or the axial load applied to the rolling surface of the outer member on the outer side increases due to turning movement of the vehicle, the opening on the outer side, which is apart from the mounting flange secured to the knuckle, can deform into a substantial elliptical shape, leading to deterioration of roundness of the rolling surface and to a decrease in the rolling fatigue life.